Prior to this invention, in a process commonly referred to as donor plasmapheresis, about 500 ml of whole blood are collected from a human donor in a blood bag. The bag is centrifuged in a place spatially separate from the blood donor to separate the plasma from the other components of the whole blood (notably, red blood cells). After centrifugation, the plasma is removed and collected. After suspension in a sterile saline solution, the remaining components are returned to the donor.
Continuous and semicontinuous centrifuging systems for donor plasmapheresis also predate this invention. All of these systems require relatively expensive apparatus. In certain cases, these systems are also time-consuming.
Underlying the present invention is the problem of providing a straight-forward, simplified plasmapheresis process which can be carried out with an extremely low expenditure on apparatus.
In accordance with the present invention, the problem is solved by positioning only a plasma filtering unit between an injection cannula and the reservoirs for collecting the plasma filtrate and the other blood components.
The use of a plasma filter is, to be sure, known in principle in therapeutic plasmapheresis. Here, blood is taken continuously from the patient by puncture of a central venous vessel and pumped at a flow rate of 50 to 250 ml/min through a "separating system" which delivers a plasma filtrate flow of 10 to 80 ml/min. Simultaneously, the withdrawn plasma is replaced by means of a suitable albumin solution (for example, human albumin or deep-frozen plasma). The corresponding treatment takes 1 to 3 hours, during which about 1 to 5 liters of plasma are exchanged. Either a continuously operating centrifuge or a so-called membrane filter can be used as the "separating system" during therapeutic plasmapheresis. Such a membrane filter has a surface area of 1000 to 5000 cm.sup.2. The membrane can be configured either as hollow fibers or as flat membranes. The membrane has a pore size which makes possible an unhampered passage of all the plasma proteins, but retains all the formed and cellular elements of the blood. Under certain geometrical and flow conditions, plasma free of cellular components and hemoglobin can be obtained.
However, such a plasma filtration process always requires blood pumps, various monitors, etc.
The use of membranes for donor plasmapheresis (for example, in U.S. Pat. Nos. 4,212,742 and 4,381,775) also always presupposes the use of relatively complicated apparatus, such as blood pumps. Furthermore, safety monitors and extensive special purpose materials (for example, tube systems with special pump segments, drop chambers with connecting pieces and transfer lines to the monitors, etc.) are used.
As a result, it can be stated that previous attempts to use a plasma filter are still more expensive than use of the above-mentioned centrifuging method.